Need help vp44 low pressure

[jdweld12v]

I have a 99 24 valve Cummins with a brand new Fass DDR p 95 with a XDP sump it drove fine for about 2 months but then I noticed pressure was low so I replace filter now at an idle I have 18 PSI and as soon as the truck gets a load on the motor it goes down to zero after about 15 secs on throttle pressure I took everything apart cleaned it the truck has 250,000 even put fass platinum on it today and it took fuel pressure the same way. I took off overflow valve and cleaned it no diffennce need help ASAP please